1. Field of the Invention
The present invention is related to light emitting devices and related driving methods, and more particularly to a light emitting device and related method thereof that dynamically changes amplitude of a driving current driving a light emitting module for reducing unnecessary power consumption.
2. Description of the Prior Art
Please refer to FIG. 1, which is a diagram of a light emitting device 100. As shown in FIG. 1, the light emitting device 100 comprises a plurality of groups of light emitting modules LED1, LED2, LED3, LED4, and a light emitting module driver circuit 110. Each light emitting module comprises a plurality of series-connected light emitting units Pcs, and is coupled to a voltage source VLED for receiving needed driving current. The light emitting units Pcs are generally realized as light emitting diodes (LEDs). The light emitting module driver circuit 110 has a plurality of driving terminals CH1, CH2, CH3, CH4 for receiving voltages VFB1, VFB2, VFB3, VFB4 through the light emitting modules LED1, LED2, LED3, LED4, respectively, for generating corresponding driving currents for driving the light emitting modules LED1, LED2, LED3, LED4. Voltage at each driving terminal CH1, CH2, CH3, CH4 is the corresponding voltage VFB1, VFB2, VFB3, VFB4.
Due to process variation, the light emitting units Pcs comprised by the light emitting modules LED1-LED4 each generate different bias voltage errors, which leads to higher voltages being generated at some driving terminals corresponding to light emitting modules having lower overall bias error, and further causes wasted power consumption in the light emitting module driver circuit 110. Taking FIG. 1 as an example, assuming voltage level of the voltage source VLED is 14.1 Volts, each light emitting unit Pcs of the light emitting module LED1 has a bias voltage error of 3.1 Volts, each light emitting unit Pcs of the light emitting module LED2 has a bias voltage error of 3.2 Volts, each light emitting unit Pcs of the light emitting module LED3 has a bias voltage error of 3.3 Volts, and each light emitting unit Pcs of the light emitting module LED4 has a bias voltage error of 3.4 Volts, the voltage VFB1 becomes 14.1−3.1×4=1.7 Volts, the voltage VFB2 becomes 14.1−3.2×4=1.3 Volts, the voltage VFB3 becomes 14.1−3.3×4=0.9 Volts, and the voltage VFB4 becomes 14.1−3.4×4=0.5 Volts. If driving currents of the light emitting modules LED1-LED4 have the same amplitude, and the light emitting module driver circuit 110 only needs 0.5 Volts to operate correctly, the light emitting module driver circuit 110 wastes power at the driving terminals CH1, CH2, CH3.
One typical solution for improving on the waste of power described above involves adding pins on the plurality of light emitting units comprised by the light emitting module for connecting to the light emitting module driver circuit 110 to keep the voltages VFB1-VFB4 at approximately 0.5 Volts. However, not only are additional pins required in design of the light emitting module driver circuit 110 which increases manufacturing costs of each light emitting module and the light emitting module driver circuit, but circuit design is also complicated.